Most useful iPhone apps?

What have you found to be the most “technically useful” iPhone app? I’m not talking about which Cabernet is the cheapest in the Chicagoland area, or a zipcode locator, etc.

i.e., I sail, so a wind speed meter, weather, chart and tide table would be useful apps. I work in the construction industry, so an engineering-calculator and clinometer/level would be useful tools. For both areas, a first-aid app might be useful as well. A plastics materials/process selection, or draft angle calculator app might be a good one for IDs.

Your thoughts?

I liked Bosch’s measurement camera (snap a photo and easily annotate dimensions). I bet their other tools are useful as well.

My favorite “technical” iPhone apps are…

Flashlight (I use this at least once a night, the most useful app I have, easily)
Unit converter

Skype is also great if you travel internationally to make very cheap calls

Dropbox is pretty awesome, as is the unit converter.

Not useful, but a great time waster: Asphalt 7!

Level (it is actually a level app. Not super accurate, but better than eyeing it)
Shazam (identifies songs playing wherever you are)
Skitch (allows you to annotate just about anything on the fly)
NBC (stream TV and news)
Uber (allows you to call a Lincoln Towne car to pick you up in most major cities, costs just a few bucks more than a cab in most cases and is great for getting to and from airports in busy cities)
LinkedIn (which acts as a nice contact book for me on the go)
Open Table

My definition of useful may be skewed…

Whatknot by Columbia is pretty cool…

iPhone Apps

Clinometer - very acurate once you calibrate, greate because it connects to a second device with the same app.
myConvert - converts everything, very extensive.
TouchCalc - super scientific calculator.